A. Field of the Invention
The invention relates generally to an optical network architecture, and more specifically to a split redundant trunk architecture that uses passive splitters and path switching, which provides for fiber cut protection and equipment failure protection.
B. Description of the Related Art
For underwater optical networks, a problem exists in shallow waters due to dragging boat anchors and the like, which may make contact with fiber optic lines and thereby cause damage or cuts to those lines. This problem also may occur for land-laid optical networks, whereby certain portions of fiber optic cable laid below ground are more susceptible to damage than other portions of the fiber optic cable. For example, if a fiber optic cable is provided between Baltimore, Md. and New York, N.Y., then there is a higher probability of damage to the fiber optic cable located at the two cities, due to building and road construction and repair, than along locations between the cities in which the fiber optic cable is laid.
Presently, fiber optic systems use one of two schemes that incorporate path diversity in regions where there is a high probability of fiber cut. In one scheme, fiber bundle legs are split at branch units and half of the fibers are routed along two different paths. In the other scheme, each wavelength division multiplexed (WDM) fiber is split/combined at the branch units by wavelength using wavelength splitters and combiners. In either case, half of the bandwidth is routed over two separate diverse paths. If one of the two fiber bundles is cut in the region where there is a high probability of fiber cuts, half of the total bandwidth is lost in the region where there is a low probability of fiber cuts. Accordingly, there is a need for a fiber optic system using a branch unit to route entire fiber bundles diversely, to avoid losing half of the bandwidth when one or more of the fiber bundles is damaged in the region where there is a high probability of fiber cuts.
Typically, conventional optical communication systems comprise a receiving node and a transmitting node (Baltimore, Md. and New York, N.Y. in the aforementioned example) connected via optical fiber. Each node contains equipment for communication via optical fiber. Such equipment includes channel equipment and WDM equipment. A fiber-bay comprises channel equipment and WDM equipment. Channel equipment is equipment that transmits and receives via a specific channel. A line unit is a repeater that optically amplifies WDM signals on an optical fiber.
The present invention is directed to an optical network architecture that operates effectively when fiber cuts occur on service lines. The optical network architecture includes a primary branch path and a secondary branch path, wherein both paths are provided on a region of high fiber cut probability of the optical network architecture, and wherein identical transmission signals are provided on the primary and secondary branch paths. The primary and secondary branch paths meet at a branch point, wherein a branch unit is located at the branch point. The branch unit includes a combiner that combines signals received on the primary and secondary branch paths, and outputs the combined signal onto a main optical path. The main optical path is located at a low probability of fiber cut of the optical ring architecture. Optionally, multiple branches may be incorporated and combiners used on subsets of fibers at each branch. The main optical path may branch multiple times, or a branched optical path may branch again for example.
In a first operation mode, at least one of the line units on the secondary branch path (preferably the last one or last few line units on that path that are closest to the branch unit) has its pump laser set to a zero or nearly-zero power output state, so as to attenuate any signals sent over the secondary branch path. In the first operation mode, each of the line units on the primary branch path has its respective pump laser set to a normal power output state. Alternatively, it can be a power output state anywhere between the zero (or near-zero) power output state and the maximum power output state (and it may even be the maximum power output state in some circumstances).
At the output of the combiner there is a 2% tap with light provided to a detector, such as a photodiode detector. If the photodiode detector does not detect any signal or if the signal quality is poor at the output of the combiner for at least a fixed time period, then it is determined that the primary branch path has a problem, and then the at least one line unit on the secondary branch path is instructed to set its pump laser to the normal power output state, so that the backup signal will be received by the combiner from the secondary branch path, due to the problem in receiving the primary (also called xe2x80x9cservicexe2x80x9d) signal from the primary branch path. The line units on the primary branch path optionally are instructed to set their respective pump lasers to the zero power output state. After the primary branch path has been fixed, then the system can be set back to a first operating mode, in which the combiner receives the primary signals from the primary branch path and not the backup signals from the secondary branch path.
In an alternative configuration, a 1xc3x972 switch (typically a high reliability switch) is provided at the branch unit instead of the passive combiner, whereby signals are provided to the two inputs of the 1xc3x972 switch from both the primary branch path and the secondary branch path. The primary branch input is provided to the output of the 1xc3x972 switch under normal operating conditions. When the output of the 1xc3x972 switch is detected to be below a threshold level, thereby indicating a problem on the primary branch path, the 1xc3x972 switch is switched to provide the input from the secondary branch path to the output of the 1xc3x972 switch. The output of the 1xc3x972 switch is provided to a main optical path, which provides fiber optic signals over a region having a low probability of fiber cuts.